1. Field of the Invention
The present invention generally relates to the processing of image coded data, and particularly relates to an apparatus and method for the decoding or code conversion of coded data with respect to still images or moving pictures.
2. Description of the Related Art
In an apparatus for decoding coded data of moving pictures, the decoding of each frame may not be completed within a predetermined time period. In such a case, the subsequent decoding process may be switched to a simplified version as disclosed in Japanese Patent Application Publication No. 2002-325257 (hereinafter, Patent Document 1). To be specific, the coded data of each frame coded by JPEG2000, which is a new international standard coding method, is subjected to decoding that starts from sub-band coefficients corresponding to lower frequencies. While this decoding process is in progress, a time lapse is monitored on a component-by-component basis or on a tile-by-tile basis. If the time lapse reaches a time limit, simplification is performed with respect to the decoding of the current component or tile.
In systems where a transmission apparatus transmits coded data of moving pictures to a reception apparatus via a network, and the reception apparatus decodes the coded data of moving pictures, there may be a need to cope with network congestion. To this end, the transmission apparatus may transmit codes of each frame in a descending order of priority in terms of image quality, and may dispose of the codes that cannot be transmitted within a frame time, as disclosed in Japanese Patent Application Publication No. 10-262245 (hereinafter, Patent Document 2). To be specific, a DCT (discrete cosine transform) is performed on a block-specific basis where one block is comprised of 8 pixels by 8 pixels. The DCT coefficients of each block are divided into a low frequency band, a middle frequency band, and a high frequency band for hierarchical coding that is independent for each frequency band. Codes of the lowest frequency band are picked up first for transmission. If no time is left, codes of higher frequency bands are disposed of.
The technology disclosed in Patent Document 1 can prevent frames from being dropped. Since the codes to be decoded and the codes to be simplified cannot be controlled through user choice, the user may not always be able to obtain reproduced images having the appearance that the user wishes.
In moving pictures of Motion-JPEG2000 in which each frame is coded according to JPEG2000, packets that constitute coded data of each frame have indexes indicative of resolution, color components, position, and image quality. In accordance with combinations of these indexes, packets can be sequenced in various orders (progression orders). Namely, in the coded data of each frame, codes are not always arranged such that the codes of lower frequencies come first as in Patent Document 1. Preference for the quality of reproduced images may differ from user to user, some attaching importance to resolution, some attaching importance to image quality, some attaching importance to color reproduction, etc. Further, the display size of images may vary. As a result, the method that decodes codes of each frame successively and switches to simplified processing after the passage of a time limit may not reproduce images having the appearance intended by the user.
The technology disclosed in Patent Document 1 may be applied to a case in which there is a need to reproduce still images of JPEG2000 or the like within a predetermined time period with sufficient real-time property. Even in this case, however, reproduced images may not always have the appearance intended by the user, which is the same as in the case of moving pictures.
The technology disclosed in Patent Document 2 serves to control the amount of codes to be transmitted by taking into account the conditions of the network, and does not guarantee that the dropping of frames is prevented in the reception apparatus (image display apparatus). Since reception apparatuses have respective decoding capabilities, the dropping of frames may occur when the decoding capability becomes insufficient or the processing load increases in a reception apparatus. Further, the user preference may not be reflected in terms of image quality, resolution, color components, etc.
If the transmission apparatus controls the amount of codes to be transmitted according to the decoding capabilities of respective reception apparatuses, it may be possible to prevent the dropping of frames. When moving pictures are distributed from the transmission apparatus to a large number of reception apparatuses, however, the load on the network increases as the data having different code amounts are redundantly transmitted with respect to the same moving pictures. It is impractical to transmit coded data in such a fashion as to reflect the needs of users of respective reception apparatuses, and, thus, it is difficult to attain image reproduction that provides the appearance intended by the user. Accordingly, it is desired to control the decoding process on a reception side, by taking into account the decoding capability, user preference, etc, rather than to control the amount of codes on a transmission side.
Accordingly, there is a need for an image processing apparatus, an image processing system, and an image processing method that can provide image reproduction properly reflecting the decoding capability, user preference, etc., with respect to coded moving pictures or coded still images.